Work to date in this laboratory has confirmed the earlier work by ourselves and others showing that the intact rat can defluorinate the organic fluoro compound, fluoroacetate. Our work has also shown that the various subcellular fractions of the rat liver possess a capability for enzymatically achieving this defluorination, activity being greatest in the 105,000 g supernatant fraction. Efforts are now being directed toward further characterizing the nature of this enzyme, including isolation, and the role of cofactors and of inhibitors. Possible in vivo inducers and inhibitors will be sought. Substrate specificity will be tested using other aliphatic fluoro compounds as well as aromatic fluoro substituted compounds. Other tissues will be examined for their capability, if any, to defluorinate organic fluoro compounds.